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Make SemIR::TypeType be an empty FacetType instruction (#7813)

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The type `type` is now a `FacetType` inst with no constraints. This
brings the model implemented in the toolchain into better alignment with
the language design. The `SemIR::TypeType` struct remains as a scope for
holding the `TypeInstId`, `ConstantId`, and `TypeId` constants, but is
not an `InstKind` anymore.

The `TypeType` inst looks a lot like singletons, but there are many
`FacetType` insts so it doesn't quite fit that model. So we put it
alongside singletons with a fixed inst id but refer to it as a more
general "builtin" inst that is not a singleton.
`Namespace::PackageInstId` is similar, and we group it with `TypeType`
conceptually as another builtin instruction with a fixed id.

No conversion is needed anymore to use a `type` as a facet, since types
also have a `FacetType` type. This simplifies and removes a number of
helpers and branches throughout the code.

The `TypeType` inst is now part of the constant store, so we end up
printing it in the constants block in every test. But it's also named
`type` rather than `%type` to preserve the majority of existing
formatting behaviour, though this does look different from other
constants.

Assisted-by: Opus 5 was used to generate a first draft and validate the
refactoring. Though nearly everything non-trivial the tool wrote has
been modified or rewritten.
This commit is contained in:
Dana Jansens
2026-09-22 15:04:40 +00:00
committed by GitHub
parent 83ca5b71e3
commit fcae9610bd
795 changed files with 9505 additions and 8048 deletions
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toolchain/check/handle_where.cpp
+1 -6
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@@ -42,10 +42,6 @@ static auto GetPeriodSelfType(Context& context,
auto frozen_const_id =
FreezePeriodSelf(context, extended_id.AsConstantId());
return context.types().GetTypeIdForTypeConstantId(frozen_const_id);
} else if (facet_type_type_id == SemIR::TypeType::TypeId) {
// The self may be `TypeType` in `type where X impls Y`, so we use an empty
// facet type.
return GetEmptyFacetType(context);
} else {
CARBON_CHECK(facet_type_type_id == SemIR::ErrorInst::TypeId,
"unexpected .Self type {0}", facet_type_type_id);
@@ -435,8 +431,7 @@ auto HandleParseNode(Context& context, Parse::RequirementImplsId node_id)
// Check lhs is a facet and rhs is a facet type.
auto lhs_as_type = ExprAsType(context, lhs_node, lhs_id);
auto rhs_as_type = ExprAsType(context, rhs_node, rhs_id);
if (rhs_as_type.type_id != SemIR::ErrorInst::TypeId &&
!context.types().IsFacetType(rhs_as_type.type_id)) {
if (!context.types().IsFacetTypeOrError(rhs_as_type.type_id)) {
DiagnoseImplsOnNonFacetType(context, rhs_node);
rhs_as_type.type_id = SemIR::ErrorInst::TypeId;
rhs_as_type.inst_id = SemIR::ErrorInst::TypeInstId;